Tubular gas heater, particularly for the heating of compressed propulsive gases for turbines



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TUBULAR GAS HEATER 0F COMPRESSED P April 25, 1950 Patented Apr. 25, 1950TUBULAB GAS HEATER, PARTICULARLY FOR THE HEATING F COMPBESSED PRO-PULSIVE GASES FOB TUBBINES Eugen Viiliger, Zurich, Switzerland, asslgnorto Aktie ngesellschaft Fuer Technische Studien,

Zurich, Switzerland, a corporation of Swltxerland Application January19, 1948, Serial No. 3,010 In Switzerland January 28, 1947 8 Claims.

'I'his invention relates to a tubular gas heater, particularly for theheating of compressed propulsive gases for turbines, in which the heatis transmitted mainly by contact.

Tubular gas heaters of this kind are used for example in thermal powerplants in which the whole or the greater part of a gaseous workingmedium, preferably air, flowing in a closed circuit is compressed in oneor more compressors, then heated by heat derived from an external sourceand afterwards expanded in one or more turbines. If the working mediumis air, it enters the tubular heater at a temperature of 200 to 400 C.and is heated therein to a temperature above 500 C.

The tubes of a heater of this kind are sub-V jected to high temperaturesand must. therefore, be highly resistant to heat. All possibleprecautions must be taken to avoid excessive local temperatures in thetubes, so that they shall not be subjected to stresses which cannot betolerated in continuous working.

In tubular heaters for plants of the kind in question, the heater tubesusually are vertical, and are arranged in radial and concentric rowsaround the axis of a centrally located furnace and waste gas chamber. Insuch an arrangement, the length of the tubes may be l0 metres or more.In order to ensure in such heaters the high velocity of the furnace andnue gases necessary to assure the most effective transmission of heat,the spacing of the tubes must be nicely proportioned and accuratelymaintained. and the stream of heating gases must be closely confined soas to assure contact with the tubes. The furnace flue gases will bereferred to hereinafter as the heating gases. In any case, the tubeshave to be arranged comparatively close to each other. This isparticularly the case in pressure fired furnaces where the specificvolume of the heating gases is less than when the pressure in thefurnace chamber is practically atmospheric. In heaters in whichtemperatures of the order mentioned exist on the two sides of the tubes,there is serious risk that the comparatively long tubes may moverelatively to each other owing to thermal expansions, thermal stressesand so on. Furthermore, the cross sectional area of the space availablefor the passage of the heating gases between the several tubes may bereduced by impurities which may be deposited thereon. Phenomena of thiskind may disturb and tend to localize the flows between the heatertubes, and this may lead to excessively high temperatures and to ajeopardizing of the safe working of the plant.

The object of the present invention is, therefore. to provide a tubulargas heater of the kind referred to, in which the spaces between theheater tubes can be made appropriate to the desired velocity of theheating gases and stable, so that they 'will remain substantially equalunder all working conditions. For this purpose. according to the presentinvention, some or all of the heater tubes are grouped in similar nests.each surrounded by a coaxial tubular jacket. The position of each jacketrelatively to the tubes which it surrounds does not change under thedifferent working conditions, and the heating gases flow necessarily andexclusively inside the jacket and in contact with the tubes. Since thedistance between individual tubes in a nest and between the tubes andthe associated surrounding jacket does not vary, the tubes in each nestwill always be impinged upon equally by the heating gases. In this way,local excessive temperatures are avoided.

Since the total cross sectional area of passage available for theheating gases between the several tubes of the nests and between saidtubes and the associated surrounding jackets is small in proportion tothe cross sectional area of the furnace and waste gas chamber, thedesired high velocity of the heating gases will be attained even thoughthe distance between the several tubes of each nest is comparativelygreat. If, however, this distance is ample, the tubes of the nest can becomparatively easily cleaned and easily replaced, each of which is anadvantage of considerable practical importance.

If the tubes be fixed (preferably by a lattice work of separatingholders) relatively to each other and to the jacket which surroundsthem, the desired spacing is ensured in a simple manner.

The various nests of tubes may be movably mounted, e. g. by suspension,so that thermal expansions of the inlet or outlet pipes (or both) forthe propulsive medium to be heated may be compensated by movement, forinstance swaying, of the nest of tubes inside the heater. If the jacketsof the tube nests are also arranged movably, for example by beingsuspended so that they can follow the movements of the tubes of thenests, the desired relative positions of the nest and jacket can bemaintained under all conditions.

The various tube nests may also, conveniently, be connected by flexibleconnecting tubes to a header at least of the inlet pipe for thepropulsive medium which is to be heated in the heater, so thatlongitudinal thermal expansions of the 3 tubes of the nests and of theinlet pipe are accommodated by the nexibility of these connecting tubes.In this way, any appreciable thermal stresses can be prevented fromarising in the inlet pipe and in the tubes of the nests.

Since the flexible connecting tubes can be connected directly to theheaders of the inlet and outlet pipes it is not necessary to provide anannular distributor or an annular collector. This is important, becausesuch annular elements are subjected to severe stresses at hightemperatures and high pressures of the propulsive medium. In most casesthey must be made as castings and homogeneity of castings of this kindcommonly leaves much to be desired. In contra-distinction thereto, theabove-mentioned nexible connecting tubes may be made oi wroughtmaterial. Another advantage is the fact that the various tube nests,together with the connecting pipes associated therewith. can be testedhydraulically separately, so that it is easy to determine whether thenests are tight and to find any nest which has become leaky.

Two examples of construction of tubular heaters according to the presentinvention are shown in a simplified form in the accompanying drawing inwhich:

Fig. 1 is a vertical axial section on the line I-I of Fig. 2 through atubular gas heater. A turbine orming part of a thermal power plantdriven by hot air, and a pipe for conducting air heated in the heaterfrom the heater to the turbine are shown in elevation.

Fig. 2 is a horizontal section on the line lI-II in Fig. 1.

Fig. 3 is a fragmentary vertical longitudinal section similar to aportion of Fig. i, showing details of a second form of construction.

Fig. 4 shows in a horizontal section on the line IV-IV of Fig. 1 detalls,on an enlarged scale.

Because ot the necessarily small scale of Figs. 1 and 2 the tube nestsare there shown as comprising only seven tubes each. A larger number oftubes would commonly be used in a nest and Fig. 4 is intended toindicate one possible arrangement. No claim is here made for the tubespacing arrangement shown in Fig. 4 since that is not the sole inventionof the present applicant and cannot be claimed herein.

The tubular gas heater I shown in Figs. i and 2 has a central furnaceand combustion chamber 2. In the lower part of the body of this heater,a, burner 3 is provided. Partly in the furnace and combustion chamber 2,concentric with the axis thereof, are arranged a number of U-shaped tubenests of whichl for the sake of clearness, only two are shown in Fig. land only three in Fig. 2. Furthermore in these two iigures, and likewisefor the sake of clearness, the corresponding tube nests have been onlypartially shown. It will be understood, however, that similar units arearranged in circular series and at substantially uniform intervalsaround the chamber 2.

Each tube nest comprises a number of tubes 5 bent into the shape of a Uand two jackets El, 62 which surround the limbs of these U-shaped tubesover a portion of their length. The jackets 61, 6 are suspended singlyby their upper ends at 52 in a chamber li called for lack of a bettername, the return chamber. This is separated by partitioning meansindicated at I both from the combustion chamber 2 and the oiitakechamber I3. In the return chamber 41 are located the arches of theU-shaped tube nests, these arches being suspended from carriers 1 whichin their turn are supported on a part 8 which forms the top cover of thefurnace and waste gas chamber 2. As above stated, the tube nests arelocated partly in the furnace and combustion chamber 2 and as will beseen by inspection of Fig. 1 that part of each nest which is enclosed inthe sleeve 62 is within the chamber 2, Whereas that part of er arnestwhich is within the sleeve 61 is in an annular surrounding chamber 43which may be called the ofltake chamber, and from which the offtake Illeads. The suspension of the tube nests above described imparts acertain amount of ilexibility to the tube nests 5 at the arch so thatwhen longitudinal thermal expansions occur, they can yield at the archesso that any such thermal expansions cannot give rise to any additionalthermal stresses in the tubes.

In the type of construction described above,

the heating gases in the chamber 2 are compelled to flow (owing to theprovision of the partitions 4 and 42 and a resilient sleeve I9connecting the lower end of the partition 42 with the shell of theheater I) inside the jackets B2, 61 which surround the tubes and thencethrough the offtake chamber 43 to the nue gas outlet Il which is formedin the outer shell of the heater I. The total heating surface isconsequently divided up into a number of separate U-shaped tube nests.In an arrangement of this kind, the distance between the several tubesof a nest and the velocity of the heating gases in the spaces within thejackets is comparatively large. The jackets 6i, 6 may be constructed astelescopic sleeves, as shown in connection with the jacket 61 on theextreme left of Fig. 1. In the latter case a short sleeve B3 providedwith a longitudinal slot 64 is mounted in such a manner on the lower endof the jacket 61 as to be adjustable in the longitudinal direction ofthe jacket, a stud passing through said slot 64 and adapted to bescrewed into said jacket allowing of fixing the sleeve 63 in theparticular position into which it has been adjusted. Thus, with the helpof the short sleeve B3 the surface of the limb of the tubes 5, which issurrounded by the left hand jacket 61 and over which the heating gasesplay, can be varied. These tubes 5 are fixed inside the several nestsrelatively to each other and to the Jackets 61 and 62 which surroundthem, in the required position by a latticework of holders 51 (see alsoFig. 4), serving as distance pieces. Three of such holders are shown inFig. l in connection with the tube nest limb shown on the extreme left.

The inlet and outlet ends of the tubes 5 of the nests are each fixednest-wise at the enlarged ends of the distributing and collectingmembers 9, I0 (see Fig. l) which, in their turn, are connected toflexible connecting tubes I I and I2. The flexible connecting tubes IIlead from the header I3 of the inlet pipe Il, and the connecting tubesI2 lead to the header I5 of the outlet pipe I6. The outlet pipe I6 leadsto the inlet connection of a turbine l1 in which the propulsive airheated in the heater expands and gives ofi' energy.

As shown in Fig. 2, the ilexible connecting tubes I I and I2 some ofwhich are of considerable length, have curved parts which are arrangedconcentrically with the axis of the heater, and the distributing andcollecting members 9 and IU oi' the various tube nests are so positionedwith regard to the pipes Il and I6 that the distances which the partialair streams have to travel in 8 the associated connecting tubes il andil are approximately the same. Consequently, the air streams aresubjected to practically equal pressure drops, a fact which contributesto uniform distribution of the air to be heated to the different tubenests.

In the tubular gas heater described. thermal expansions of the exhaustpipe I6, which start from a fixed point Il outside the heater, areaccommodated inside the heater by the swaying movements of the nesttubes l connected to the header Il by the flexible connecting tube il,the

jackets I being thereby compelled by the distance pieces B1 to followthe movements of the tube nests i. The position of the jacket irelatively to the associated nest tubes consequently undergoes no changeunder different working conditions so that the tubes of the nest willalways be impinged upon by the heating gases equally.

The flexible connecting tubes Il and i! also compensate longitudinalthermal expansions of the nest tubes 5 and of the inlet and exhaustpipes I4 and IB, which likewise contributes to the fact that noappreciable thermal stresses can arise in the pipes Il, IB and ln thenest tubes 5.

Instead of connecting the tubes of the nests to the inlet and exhaustpipes for the propulsive medium to be heated in the heater, the tubes 2Bof the nests can be connected in the manner shown in Fig. 3 directly tothe header 2i of the inlet pipe and the header 22 of the exhaust pipe.The jacket 23 which surrounds the associate tubes 20 of a nest issuspended by its upper end at the point 24 in this construction also.This point 2l lies in a space or chamber 25 whichlis separated by sheetmetal partitions 21 from the furnace and waste gas chamber 2E. 28denotes holders forming distance pieces which x the nest tubes 20 in thenecessary position both relatively to each other and to the jacket 23.If the header 22 is subjected to thermal expansion and, as is usuallythe case, from a xed point situated outside the heater, the tubes 20 cansway out correspondingly, the jacket 23 being compelled to follow thesemovements of the tubes 20. Thus the tubes Iii are impinged upon by thegases in a substantially equal manner, so that no appreciable thermalstresses can consequently arise in them.

Realization of the invention is not limited to furnaces of the kindreferred to herein, since the kind of furnaces plays no part in itsapplication. The invention can thus be adopted in conjunction withfurnaces for solid, liquid or gaseous fuels.

What is claimed is:

1. A gas heater comprising in combination a furnace structure includinga shell and partitions which divide the space within the shell into atleast two chambers, namely a combustion chamber, and an oiItake chamberhaving an oiitake for products of combustion; means for causingcombustion in said combustion chambers; a piu rality of heat exchangeunits, a substantial part of each of which is located within saidcombustion chamber, each said unit comprising a group of generallyparallel spaced tubes and means forming inlet and outlet manifoldsarranged to connect the tubes of the unit for parallel iiow of gas to beheated: at least one open-ended flowconiining Jacket for each unit, eachjacket surrounding the corresponding group of tubes, said jacketsdefining enclosed flow paths for products of combustion extending in thedirection of the length of the surrounded tubes and each such pathcommunicating at its entrance end with the combustion chamber and at itsdischarge end with the oiftake chamber; spacing means serving tomaintain the spacing of the tubes of each unit from one another and fromthe associated jacket; inlet and discharge connections leadingrespectively to and from said manifolds, and serving to connect thevarious units in parallel; and means for supporting said jackets uponsaid partitions of the furnace structure.

2. The combination defined in claim l in which means are provided bywhich each group of spaced tubes is movably suspended from the furnacestructure near the upper extremity of the unit. and by which theassociated jacket is movably supported.

3. The combination defined in claim i in which means are provided bywhich each group of spaced tubes is movably suspended from the iurnacestructure near the upper extremity of the unit. and by which theassociated jacket is movably supported at its upper end so as to becapable of pendulous motion with the associated tube group. and theinlet and discharge connections to the manifolds are flexible.

4. The combination defined in claim 1 in which at least some of theflow-confining jackets comprise telescoping sections whereby theeffective length of the jacket is adjustable.

5. The combination dened in claim l in which the shell of the heater isgenerally cylindrical and the oiitake chamber is annular in form andsurrounds at least a portion of the combustion chamber.

6. A gas heater comprising in combination a furnace structure includinga generally cylindrical shell and partitioning means which divide thespace within the shell into a central combustion chamber, a surroundingofftake chamber having an oiftake for products of combustion, and areturn chamber which overlies at least portions of the combustionchamber and of the oiitake chamber; means for causing combustion in saidcombustion chambers; a plurality of heat exchange units each unitcomprising a group of generally parallel spaced tubes bent to inverted Uform and means forming inlet and outlet manifolds located one in theoiftake chamber and the other in the combustion chamber and each at thelower extremity of the corresponding arm of the U. said manifoldsconnecting the tubes for parallel flow of gas to be heated and the bentportion of the tubular unit being located in said return chamber withthe arms oi the U passing downward therefrom into the combustion andoitake chambers respectively. through openings provided therefor in saidpartitioning means; means by which the heat exchange units are suspendedfrom the furnace structure; an open-ended tlow-conning jacket for eacharm of each unit, each jacket surrounding the corresponding group oftubes, and the jackets enclosing a flow path for products of combustionextending in the direction of the length of the tubes from thecombustion chamber into the lower end of one jacket, through the jacketto the return chamber and thence downward through another jacket intothe offtake chamber; spacing means serving to maintain the spacing ofthe tubes of each unit from one another and from associated jackets;inlet and discharge connections leading respectively to and from saidmanifolds and arranged to connect the various units in parallel; andmeans for movably sustaining said jackets at their upper ends upon themargins of corre sponding openings in said partitioning means.

accusa* '7. The combination defined in claim 6 in which the suspendingmeans for the heat exchange units are mounted in said return chamber andengage said heat exchange units at the bends therein; and the inlet anddischarge connections to the various manifolds take the form ofindividual curved tubes connected respectively to supply and dischargeconnections adjacent the furnace shell.

8. The combination defined in claim 6 in which the inlet and dischargeconnections to and from the various manifolds take th form of individualcurved tubes connected respectively to supply and discharge connections,said"` individual curved tubes being so graduated in length that thelength of the inlet connection plus the length of the flow 15 paththrough the unit plus the lensth olf-the?" discharge connection issubstantially uniform` for all units.

EUGEN VILLIGER.

REFERENCES CITED The following references are o! record in the ille ofthis patent:

UNITED STATES PATENTS

